These modelled values were calculated by the NOAA-GLERL Large Lake Thermodynamic Model using observed values for wind speed, air temp, cloud cover, and dew point. View the following literature for more information:
CROLEY, T.E.II. Lumped modeling of Laurentian Great Lakes evaporation, heat storage, and energy fluxes for forecasting and simulation. NOAA Technical Memorandum ERL GLERL-70, Great Lakes Environmental Research Laboratory, Ann Arbor, MI (PB89-185540/XAB) 48 pp. (1989).
CROLEY, T.E.II. Verifiable evaporation modeling on the Laurentian Great Lakes. Water Resources Research, 25(5):781-792 (1989).
CROLEY, T.E., II, and R.A. ASSEL. A One-Dimensional Ice Thermodynamics Model for the Laurentian Great Lakes. Water Resources Research, 30(3):625-639 (1994).
From CoastWatch at GLERL:
The Great Lakes Surface Environmental Analysis (GLSEA2) is a digital map of the Great Lakes surface water temperature and ice cover which is produced daily at the NOAA Great Lakes Environmental Research Laboratory (GLERL) in Ann Arbor, Michigan through the NOAA CoastWatch program. The GLSEA is stored as a 1024x1024 pixel map in PNG format, suitable for viewing on PCs and workstations with readily available software.
The lake surface temperatures are derived from NOAA polar-orbiting satellite imagery obtained through the Great Lakes CoastWatch program. The addition of ice cover information was implemented in early 1999, using data provided by the National Ice Center (NIC). Lake surface temperatures are updated daily with information from the cloud-free portions of the previous day's satellite imagery. If no imagery is available, a smoothing algorithm is applied to the previous day's map. Ice information will then be added, using the most recent Great Lakes Ice Analysis produced by NIC, daily during the ice season.
Leshkevich, G.A., D.J. Schwab, and G.C. Muhr. Satellite environmental monitoring of the Great Lakes: Great Lakes CoastWatch Program update. Marine Technology Society Journal 30(4):28-35 (1997).
Schwab, D.J., G.A. Leshkevich, and G.C. Muhr. Satellite measurements of surface water temperature in the Great Lakes: Great Lakes CoastWatch. Journal of Great Lakes Research 18(2):247-258 (1992).
Leshkevich, G. A. and S. Liu. Environmental monitoring of the Great Lakes using CoastWatch data and JAVA GIS. Backscatter Magazine, Spring 2003:13-16 (2003).